1. Field of the Invention
The invention relates to electrochemical devices, in particular of the type comprising at least one carrier substrate provided with a stack of functional layers comprising at least one electrically conducting layer and at least one electrochemically active layer. More particularly, the invention envisages electrically controllable systems having variable optical and/or energy properties, in glazing applications or mirror applications.
2. Discussion of the Background
The reason for this is the increasing demand for so-called xe2x80x9csmartxe2x80x9d glazing whose properties are capable of variation.
Thus, from the thermal standpoint, glazing whose transmission/absorption can be varied within at least part of the solar spectrum allows the solar heat influx into rooms or passenger areas/compartments to be controlled when it is fitted as external glazing in buildings or as windows in means of transportation of the type comprising cars, trains, aircraft, etc., thus allowing avoidance of excessive heating of the latter in strong sunlight.
From the optical standpoint, the glazing allows the visibility to be controlled, and when it is installed as exterior glazing this makes it possible to prevent glare in strong sunlight. It may also have a particularly advantageous shutter effect, either used, as exterior glazing or if used as interior glazing, for example for equipping internal partitions between rooms. (offices in a building), or for isolating compartments in trains or aircraft.
There are many other applications: for example, glazing having variable light transmission/reflection may be used to make rear-view mirrors, which can darken as required in order to prevent dazzling of the driver of the car. They may also be used for road sign panels, or for any display panel, for example so as to reveal the pattern or message only intermittently, in order to attract greater attention.
One particularly interesting application of systems having variable light absorption relates to display screens, in particular those with which televisions and computing hardware are equipped. The reason for this is that this type of glazing makes it possible to improve the contrast of the image, especially taking ambient brightness into account.
The interest which glazing of this type can arouse is the reason for the many systems which have already been studied.
Two systems are of more particular interest for the invention: viologenic systems and electrochromic systems.
Viologenic systems allow the transmission or absorption of glazing which incorporates them to be modified, essentially in the visible region. They generally comprise just one xe2x80x9cactive layerxe2x80x9d based on polymer, on gel or on liquid comprising a so-called cathodic active material, such as viologenic molecules, together with a so-called anodic active material, such as dimethylferrocene or phenazines. Some examples of these are described in patents EP-0 612 826 and U.S. Pat. No. 5,239,406.
As is known, electrochromic systems include a layer of an electrochromic material capable of reversible and simultaneous insertion of ions and electrons and whose oxidation states corresponding to the inserted and ejected states have a distinct colour, one of the states having higher light transmission than the other, the insertion or ejection reaction being controlled by a suitable electrical supply. The electrochromic material, usually based on tungsten oxide, must therefore be placed in contact with a source of electrons, for example a transparent electrically conducting layer, and with a source of ions (cations or anions), for example an ionic conductive electrolyte.
It is moreover known that, in order to secure at least about a hundred switching operations, there must be associated with the layer of electrochromic material a counterelectrode which is itself capable of reversibly inserting cations, symmetrically with respect to the layer of electrochromic material so that, macroscopically, the electrolyte appears as a single ion medium.
The counterelectrode must consist of a layer which is either neutral in colour or at least transparent or with little colour when the electrochromic layer is in the coloured state. As tungsten oxide is a cathodic electrochromic material, that is to say a material whose coloured state corresponds to the most reduced state, the material used for the counterelectrode is generally an anodic electrochromic material based on nickel oxide or, on iridium oxide. It has also been proposed that the material used be optically neutral in the oxidation states concerned, for example cerium oxide or organic materials such as electronically conductive polymers (polyaniline, etc.) or Prussian blue.
A description of systems of this type is found, for example, in European Patents EP-0 338 876, EP-0 408 427, EP-0 575 207 and EP-0 628 849.
Currently, these systems may be arranged in two categories, according to the type of electrolyte which they use:
either the electrolyte is in the form of a polymer or of a gel, for example a polymer exhibiting protonic conduction, such as those described in European Patents EP-0 253 713 and EP-0 670 346, or a polymer exhibiting lithium-ion conduction, such as those described in Patents EP-0 382 623, EP-0 518 754 or EP-0 532 408,
or the electrolyte is an inorganic layer which is ionically conductive but electronically insulating; these systems are referred to as xe2x80x9call-solidxe2x80x9d electrochromic systems. For the description xe2x80x9call-solidxe2x80x9d applied to an electrochromic system reference may be made to the European Patent Applications EP-0 867 752 and EP-0 831 360.
There are other types of electrochromic systems. Mention may therefore be made of xe2x80x9call-polymerxe2x80x9d electrochromic systems, where two electrically conducting layers are arranged on either side of a stack comprising a cathodic-colouring polymer, an electrically insulating but ionically conductive polymer (very particularly conductive for H+ or Li+) and finally an anodic-colouring polymer (such as polyaniline or polypyrrole).
Finally, there are also xe2x80x9cactivexe2x80x9d systems in the sense of the invention which combine viologenic materials and electrochromic materials, for example having the sequence conducting electrode/inorganic layer or polymer having electrochromic properties/ layers (liquid, gel, polymer) having viologenic properties/conducting electrode.
These systems comprising reversible insertion material(s) are of particular interest in the sense that they allow modification of absorption within a wavelength region which is wider than that for viologenic systems: they can absorb variably not only in the visible region but also, in particular, in the infrared region, and this can make them useful optically and/or thermally.
A point which is common to these different systems, described below by the term xe2x80x9cactivexe2x80x9d systems is that their transmission/absorption state is controlled by applying a potential difference to their terminals, generally formed by two electrically conducting layers between which the electrochemically active layer(s) lie(s). When these systems are part of xe2x80x9cactivexe2x80x9d glazing, the electrically conducting layers are preferably transparent (or at least one of them is transparent if the other is chosen to reflect in the visible region in a mirror application). The material needed when selecting the nature of these electrically conducting layers has therefore to be both sufficiently conductive and sufficiently transparent in the ranges of thickness usually encountered in the field of thin layers. The selection usually concentrates on a doped metal oxide material, such as fluorine-doped tin oxide (SnO2:F) or tin-doped indium oxide (ITO), which may be laid down on various substrates, either hot (in particular by pyrolysis on glass, as in the CVD method) or cold (vacuum techniques of cathodic sputtering type).
However, it has been found that, at thicknesses at which they are still transparent, layers based on this type of material are not fully satisfactory even though they do permit the functioning of active systems.
They are insufficiently conducting and increase the response time of the active systems on application to their terminals of an electrical supply appropriate to change their transmission/adsorption state (the state described below for greater simplicity by the term xe2x80x9ccolorationxe2x80x9d state, even if the modification of properties also operates outside the visible region).
In addition to the fact that they reduce the switching speed of the systems (xe2x80x9cswitchingxe2x80x9d or xe2x80x9cresponse timexe2x80x9d being the period of time necessary for the entire active system to have changed its coloration state) the layers contribute to the creation of an edge phenomenon, i.e. non-uniformity in the change of state of the system within its surface, with a change in xe2x80x9ccolorationxe2x80x9d in the sense of the invention which is almost immediate in the zones near to the current leads supplying the electrically conducting layers, arranged at the periphery of the systems, and which propagates progressively toward the centre of the surface of the active systems. Now, in certain applications, in particular glazing for buildings or automobiles, the final user generally desires the fastest possible response time and may, in addition, prefer a progressive, uniform change of coloration over the entire surface of the active glazing.
The object of the invention is therefore to improve the performance of the electrically conducting layers of the xe2x80x9cactivexe2x80x9d systems defined below, and very particularly of xe2x80x9cactivexe2x80x9d glazing comprising these latter, the improvement being aimed in particular at their electrical conductivity in association with their optical properties.
A first object of the invention is an electrochemical device, in particular an electrically controllable system having variable energy and/or optical properties, including at least one carrier substrate provided with a stack of functional layers comprising at least one electrically conducting layer A based on metal oxide(s) and at least one electrochemically active layer F. The invention consists in the fact that said layer A is part of a multicomponent electrode E combining with the layer A at least one higher-conductivity material B and/or at least one network C of conducting wires or conducting strips.
For the purposes of the invention, xe2x80x9chigher-conductivityxe2x80x9d describes a material B which, in the form of a layer, has a surface resistance xe2x80x9csurface Rxe2x80x9d lower; than that of the layer A. For the purposes of the invention, again, xe2x80x9ccombinationxe2x80x9d indicates that the elements concerned are electrically connected one to the other, either by direct contact or else through conducting elements/layers.
The reason for this is that increasing the thickness of the layer A to heighten its conductivity (i.e. lower its surface resistance) is a limited solution: firstly in terms of cost and of manufacturing time for the layer in question and secondly in terms of optical appearance: above a certain thickness layers of this type begin to absorb in the visible region. Now, very particularly for active glazing, as required by its application, it is generally desirable to ensure maximum light transmission in the xe2x80x9cuncolouredxe2x80x9d state. The solution according to the invention has therefore consisted in reconciling conductivity and transparency by developing two versions, alternative or cumulative.
The material B defined above may be combined with the layer A in two different ways: according to a first version it may be in the form of at least one layer combined with A and in electrical contact therewith.
The characteristics and thicknesses of the layers may then be optimized so that the multicomponent electrode which combines them has, overall, the required levels of transparency and surface resistance.
A second version consists in incorporating the material B in the layer A, in particular in the form of fibres or of small particles. It is also possible to use a layer A based on doped oxide, for example SnO2: F, which is laid down in a known manner by liquid pyrolysis using appropriate organometallic precursors and adding, to the liquid phase comprising these precursors, fibres or metallic particles, or spraying them at the surface of the substrate simultaneously with the liquid phase (for example fibres with a diameter of the order of 10 xcexcm and a length of about 1 mm). The location of the fibres in the layer is random, xe2x80x9cpercolatingxe2x80x9d over the surface of the substrate coated in this way. In this situation the doped metal oxide of the layer A also fulfils the function of fixing the metallic fibres B.
The third version consists in combining the layer(s) of type A with a network of conducting elements, in particular based on a metal of intrinsically higher conductivity than the material of type A. Actually, as described in detail below, this network may be composed of linear elements visible to the eye at close quarters but sufficiently discreet to be compatible with most of tie applications envisaged in glazing for buildings or for vehicles. It is then advantageous for these elements to be dimensioned and arranged so that their visibility is as low as possible. Generally, success can be obtained by making this network almost impossible to discern, at least when the system is in the coloured state.
It will be noted that, in the same active system, these different versions are alternative or cumulative.
The point common to these versions is that the additional conducting element, namely the material B or the network C, allows the overall electrode formed in this way to overcome a threshold of conductivity, so that the entirety of the electrode experiences the same potential difference at almost the same time as soon as the voltage is applied to the system, and this significantly reduces the switching time and reduces or even eliminates the xe2x80x9ccoloration frontxe2x80x9d effect mentioned above. And this highly interesting technical result is not obtained by compromising the optical quality of the system if:
either this additional element itself has little or no absorbency in the visible region, so that being transparent it does not noticeably change the appearance of the glazing or the range of transmission/absorption within which variation can be made using the action of an electrical supply (type B layer),
or this additional element is sufficiently discreet not to have any adverse effect on the overall aesthetics of the active system (type C network).
The layer(s) A is/are advantageously based on metal oxide rendered conductive by doping. This may in particular be doped tin oxide, in particular doped with a halogen of the type comprising fluorine (SnO2:F) or with antimony (SnO2:Sb), or zinc oxide doped, for example, with aluminium (ZnO:Al) or with tin (ZnO:Sn) or with fluorine (ZnO:F) or with indium (ZnO:In). It may also be tin-doped indium oxide, such as ITO.
According to the first version the layer(s) B is/are advantageously essentially metallic, in particular based on at least one noble metal or based on an alloy comprising a noble metal of the type comprising silver Ag or gold Au or copper Cu or aluminium Al. The layer selected is preferably one based on an alloy of silver with another metal, such as nickel or titanium. The reason for this is that it makes the layer much less susceptible to oxidation, in particular when it is in electrical contact with layers of electrochromic materials in an xe2x80x9call-solidxe2x80x9d system. Gold is a material even less susceptible than pure silver to oxidation, but it is less satisfactory from an optical standpoint, being less neutral in transmission. The combination of a type A layer and a type B layer is of particular interest: as already seen, it allows sufficient enhancement of the electrical conductivity of type A layers with layers B which have low thickness and therefore no excessive adverse optical effect. This is also a novel means of incorporating layers B in electrodes, in particular silver layers, the use of which has hitherto posed the problem of protecting these from attack, in particular by oxidants. Thus type A layers can be used to xe2x80x9cprotectxe2x80x9d type B layers, in particular from oxidation/degradation, the layers A having a double function as protection and electrical conductor, indeed a triple function with an added optical function when the thicknesses of the type A layers are adjusted as a function of those of the type B layers to optimize the optical appearance of the entirety by interference interaction between these different layers. It is thus possible, for example, to reduce the light reflection induced by the layer B.
As mentioned above, the characteristics of the layers incorporated in the multicomponent electrodes of the invention are chosen so that they are essentially transparent in the visible region.
According to the second version the small elements of the type comprising fibres, particles or grains which are incorporated in the layer may be of the metal also mentioned for the layer B: Ag, Au, Cu, Al, or else based on steel, Cr, Ni alloy, etc.
In a first embodiment of the third version of the invention, the network C advantageously includes a plurality of conducting strips, in particular essentially parallel each to the other and obtained by screen printing, using a paste-like suspension of silver-type metal and a low-melting-point frit in an organic binder. The screen printing may be carried out on a glass-type carrier substrate, which may then be covered with at least one electrically conducting layer A in order to form an electrode according to the invention. One version consists in carrying out the opposite operation, namely laying down the network C on the electrically conducting layer A. The technique of deposition by screen printing on glass is known per se for laying down conducting networks for other applications, and very particularly for forming heater networks for vehicle glazing, in order to allow demisting or defrosting by resistance heating. For further details of this technique reference may be made, for example, to the patents FR-1 464 585 and EP-0 785 700. Since the desired function here is different, the specialist will need to determine the strip width and the strip spacing which are most appropriate to give the best compromise between conductivity and aesthetics (for example a strip width of 0.1 to 0.5 mm and a strip spacing of 1 to 5 mm).
According to a second embodiment, the network C includes a plurality of essentially metallic conducting wires, preferably surface-laid on a sheet based on thermoplastic polymer. As for the first embodiment, there are known techniques for laying down conducting wires on films, for example polyvinyl butyral films, which are combined by lamination with glass to form laminated glazing, the network having a demisting/defrosting function by means of resistance heating. It is therefore possible to adapt these techniques, optionally with adjustment of the configuration, the spacing and the dimensioning of the wires, to design a network which, combined with the thermoplastic film, will be pressed onto the type A layer, itself arranged on the remainder of the stack of functional layers of the active system, in particular by a lamination technique. For further details concerning the technique of laying down these wires reference may be made, in particular, to the patents EP-0 785 700, EP-0 553 025, EP-0 506 521 and EP-0 496 669. The wires may be laid down in the form of curves or straight lines. In outline the process consists in using a heated pressure roll to press the wire onto the surface of the thermoplastic film, the wire being fed to the pressure roll from a supply reel with the aid of a wire-guiding device.
According to another embodiment, there may be a wider interpretation of the network C, and this may in particular be two-dimensional, in the form of a fabric, net or nonwoven obtained by weaving or knitting and sufficiently fine and/or with a sufficiently high mesh size not to impair visibility. There may also be introduction of this type of material between the sheet based on thermoplastic polymer which serves in particular for the lamination of the system and the type A layer.
This type of material, which is flexible, may preferably be obtained using metallic wires, in particular with a diameter between 10 xcexcm and 100 xcexcm. The mesh size, the spacing of the knit and the type of weaving may be modified as appropriate. Thus, preference is given to wires with a diameter of from 15 to 25 xcexcm with a knit structure and with mesh spacings of the order of from 1 to 3 mm.
The xe2x80x9cnetworkxe2x80x9d also comprises metallic layers of sufficient thickness to give a severe reduction in light transmission, or even to be opaque, and which undergo treatments so that they are rendered discontinuous. This may be a treatment by etching a metallic layer laid down by cathodic sputtering, where the etching may be effected by laser in order to leave xe2x80x9cwiresxe2x80x9d (for example of width 0.3 mm and separation of 1.5 mm) or a two-dimensional grid. The metal in the layer may be stainless steel, copper, silvered copper, aluminium, or gold in particular.
It is also possible to treat the metallic layer by perforating it to give regularly distributed openings. This metallic layer may also be replaced by a perforated metallic sheet inserted been the stack of the active system and the lamination intercalation (a sheet thicker than a layer, for example with a thickness of from 10 to 100 xcexcm).
If the substrate is sufficiently rigid, as is glass, it is also possible to adapt the screen-printing technology described above by etching shallow lines on the surface of the glass, parallel lines which will be filled with the screen-printing paste, giving a screen-printed network which is particularly discreet and is at the same time conducting.
Provision may advantageously be made for the two-dimensional network C of grid or fabric type, even in the event that it is self-supporting, to be embedded at the surface of the thermoplastic polymer film serving for lamination of the glazing. It may have been preembedded, like the conducting wires mentioned above. It may also be embedded in the film during the course of the lamination.
Rather than the screen printing of conducting wires, these wires may be laid down, for example as tungsten wires, on substrates which may have been previously provided with a conducting layer of doped metal oxide type, and retained at the periphery of the glazing by means of a suitable double-sided adhesive, which can also have a sealing function.
In one preferred embodiment of the first version according to the invention, the multicomponent electrode comprises at least one layer A and at least one layer B in electrical contact, at least one of these optionally being in contact with at least one layer D of dielectric material, and all of the superposed layers A, B and D preferably forming a stack of layers with interference interaction. The stacks of layers found here may actually be rather similar to those used as low-emission/solar protection stacks for glazing in buildings or vehicles, stacks of the following outline type:
dielectric coating{circle around (1)}/silver/dielectric coating{circle around (2)}, with optionally a fine layer of protective metal at the Ag/dielectric interface. The dielectric coating may be a layer or superposed layers based on metal oxide (SnO2, ZnO, TiO2, SiO2, Ta2O5, Nb2O5, etc.) or silicon nitride or oxynitride (SiON, Si3N4) or a mixture. Reference may be made, for example, to the stacks described in patents EP-0 611 213, EP-0 678 484 and EP-0 718 200, or else those used to equip glazing marketed in the xe2x80x9cPlanithermxe2x80x9d range by Saint-Gobain Vitrage. The application here is different and it is therefore necessary to adapt these stacks by replacing one or both of the abovementioned dielectric coatings {circle around (1)} and {circle around (2)} with one or more doped oxide conducting layers (of type A). The interposition of electrically insulating layers between the superposed conducting layers and the rest of the active layers in the system must be avoided. On the contrary, there is no reason not to add dielectric insulating layers to the conducting stacks of type (layer A/layer B) or (layer A/layer B/layer A) on the opposite side from the remainder of the functional layers, for example on the side facing the carrier substrate. The resultant stacks may be of the type:
substrate/dielectric D/layer B (Ag type)/layer A (ITO type)/remainder of the functional stack in the active system.
These layers D then fulfil an optical function and/or a function of anchoring type B layers to the substrate, and/or fulfil a function as a barrier to the migration of species coming from the substrate (for example alkalis coming from the glass). As mentioned above, the dielectric materials may be in the form of oxide, oxycarbide or oxynitride of a metal or of silicon, or be based on silicon nitride.
Some examples of this type of electrode are ITO/Ag/ITO, Ag/ITO and dielectric/Ag/ITO with optional interposition of thin layers of partially oxidized metal at the Ag/ITO interface, the second ITO layer protecting the silver layer while participating in the electrical conductivity of the entirety.
The multicomponent electrodes according to the invention are provided with appropriate current leads of a type known in the art, in particular in the form of metal braids or shims.
As mentioned above, the invention is particularly applicable to an electrochromic system with at least one carrier substrate and a stack of functional layers comprising at least, in succession, a first electrically conducting layer, an electrochemically active layer liable to reversible insertion of ions, such as H+, Li+ or OHxe2x88x92, of anodic or, respectively, cathodic electrochromic material type, a layer of electrolyte, a second electrochemically active layer liable to reversible insertion of ions, such as H+, Li+ or OHxe2x88x92, of cathodic or, respectively, anodic electrochromic material type, and a second electrically. conducting layer, with at least one of the electrically conducting layers in the form of a layer A based on metal oxide(s) and being part of a multicomponent electrode E.
It is also applicable to any viologenic system with at least one carrier substrate and a stack of functional layers comprising at least, in succession, a first electrically conducting layer, a film having viologenic properties in the form of a polymer, of a gel or of a suspension in a liquid medium, and a second electrically conducting layer, with at least one of the two electrically conducting layers being of type A based on metal oxide(s) and being part of a multicomponent electrode E.
The invention thus relates to all the types of xe2x80x9cactivexe2x80x9d system described in the preamble to the present application.
According to the invention it is advantageous for the stack of functional layers to be arranged between two substrates, each of which may be rigid, of glass type or rigid polymer, such as polycarbonate or PMMA (methyl polymethacrylate), or semi-rigid or flexible of PET type (polyethylene terephthalate), all of these being preferably transparent. They may also be absorbent or otherwise.
Another subject of the invention is glazing incorporating the device/active system described above, said device using as carrier substrate at least one of the rigid constituent substrates of the glazing and/or at least one flexible substrate combined by lamination to one of the rigid constituent substrates of said glazing.
Another subject of the invention is the use of the device and of the glazing described above for making glazing for buildings, in particular exterior glazing or internal partition glazing or door glazing or roof windows, glazing equipping internal partitions or windows or roof windows in means of transport of the type comprising trains, aircraft, cars and boats, glazing for display screens of the type comprising computer or television screens, or touch screens, or spectacles, camera lenses or protection for solar panels.
Another subject of the invention is the use of the device described above for making electrochemical energy-storing devices of battery or fuel-cell type, and the batteries and cells themselves. The reason for this is that it is of very particular interest for battery applications to use the version of the invention consisting in the use of an electrode comprising a perforated metallic sheet or metallic grid. Since batteries are frequently produced on rather thin plastic substrates (of PET type, about 30 xcexcm) if the conducting layers are flexed they are in danger of losing their electrical continuity. A thicker metallic xe2x80x9cgridxe2x80x9d allows this continuity to be assured more effectively.